There are a variety of hydrocarbon conversion processes, and these processes utilize different catalysts.
Alkylation is typically used to combine light olefins, for example mixtures of alkenes such as propylene and butylene, with isobutane to produce a relatively high-octane branched-chain paraffinic hydrocarbon fuel, including isoheptane and isooctane. Similarly, an alkylation reaction can be performed using an aromatic compound such as benzene in place of the isobutane. When using benzene, the product resulting from the alkylation reaction is an alkylbenzene (e.g. ethylbenzene, cumene, dodecylbenzene, etc.).
The alkylation of paraffins with olefins for the production of alkylate for gasoline can use a variety of catalysts. The choice of catalyst depends on the end product a producer desires. Typical alkylation catalysts include concentrated sulfuric acid or hydrofluoric acid. However, sulfuric acid and hydrofluoric acid are hazardous and corrosive, and their use in industrial processes requires a variety of environmental controls.
Solid catalysts are also used for alkylation. However, solid catalysts are generally rapidly deactivated by the presence of water, which may be present in the feed.
Processes for the oligomerization of light olefins (e.g. ethylene, propylene, and butylene) to produce higher carbon number olefin products (e.g. C6+ olefins) are well known. Oligomerization processes have been employed to produce high quality motor fuel components as well as petrochemicals from ethylene, propylene, and butylene. These oligomerization processes are also referred to as catalytic condensation and polymerization, with the resulting motor fuel often referred to as polymer gasoline. In the refining area, methods have been continually sought to improve the octane number of the gasoline boiling range oligomerization products. This octane enhancement is generally realized through the improvement of the oligomerization reaction selectivity to enhance the representation of high octane blending components (e.g., branched olefins) in the product slate. The ability of the process to better target specific carbon number species is also a primary consideration when highly purified chemical grade products are desired. In any case, the enrichment of product slate to the targeted species, in addition to providing a higher quality and quantity of useable products, also benefits catalyst life. This is due to the reduction in non-selective heavy oligomers that condense into coke which ultimately covers the catalyst.
Known catalysts for effecting the oligomerization reaction include heterogeneous catalysts such as solid acids and homogeneous catalysts, in particular boron trifluoride as described, for example, in U.S. Pat. No. 3,981,941. Other catalysts fall within the description of mild protonic acids, generally having a Hammett acidity function of less than −5.0. Particularly preferred among these are solid phosphoric acid (SPA) catalysts having as a principal ingredient an acid of phosphorous such as ortho, pyro, or tetraphosphoric acid. Details of SPA catalysts are provided in the prior art, for example in U.S. Pat. No. 5,895,830. The use of zeolites as oligomerization catalysts is also described, along with various catalyst treatment methods designed to improve performance in U.S. Pat. Nos. 4,547,613, 4,520,221, 4,642,404, and 5,284,989, for example. Another type of catalyst which may be employed comprises a supported metal compound, as described in U.S. Pat. Nos. 3,562,351, 3,483,269, 3,592,869 3,644,564, 3,679,772, 3,697,617, 3,663,451, 3,755,490, 3,954,668, 3,170,904, 3,170,906. Unsupported metal catalysts are described in, U.S. Pat. Nos. 3,155,642, 3,155,642, 3,457,321, 3,483,268, and 3,505,425, and British Patent 1,123,474. U.S. Pat. No. 4,757,042 describes a catalyst comprising a complex of nickel or palladium, certain fluoro-organo sulfur ligands and an organo-metallic reducing agent.
The disproportionation of paraffins (e.g., isopentane (iC5)) involves reacting two moles of hydrocarbon to form one mole each of two different products, one having a carbon count greater than the starting material and the other having a carbon count less than the starting material. The total number of moles in the system remains the same throughout the process, but the products have different carbon counts from the reactants.
Suitable catalysts include, but are not limited to, HF, sulfated zirconias, AlCl2/SiO2, zeolites, ionic solids, platinum on chlorided Al2O3/Ga2O3 supports, supported ionic liquids, Pt/W/Al2O3, HF/TiF4, or combinations thereof.
Isomerization of linear paraffins to their branched isomers increases their octane number and thus their value to a refiner. Isomerization processes involve reacting one mole of a hydrocarbon (e.g., normal pentane) to form one mole of an isomer of that specific hydrocarbon (e.g., isopentane). The total number of moles remains the same throughout this process, and the product has the same number of carbons as the reactant.
Current isomerization processes use chlorided alumina, sulfated zirconia, or zeolites in conjunction with platinum. Process temperatures range from about 120° C. for chlorided alumina up to about 260° C. for zeolite type catalysts. These reactions are run at temperatures which allow the feed to reach equilibrium. At lower temperatures, the equilibrium favors the branched isomers possessing the higher octane number.
Acidic ionic liquids can be used as an alternative to the commonly used strong acid catalysts in hydrocarbon conversion processes. Ionic liquids are catalysts that can be used in a variety of catalytic reactions, including the alkylation of paraffins with olefins. Ionic liquids are salts comprised of cations and anions which typically melt below about 100° C.
Ionic liquids are essentially salts in a liquid state, and are described in U.S. Pat. Nos. 4,764,440, 5,104,840, and 5,824,832. The properties vary extensively for different ionic liquids, and the use of ionic liquids depends on the properties of a given ionic liquid. Depending on the organic cation of the ionic liquid and the anion, the ionic liquid can have very different properties.
Although ionic liquid catalysts can be very active, alkylation reactions need to be run at low temperatures, typically between −10° C. to 30° C., to maximize the alkylate quality. This requires cooling the reactor and reactor feeds, which adds substantial cost to an alkylation process utilizing ionic liquids in the form of additional equipment and energy. The most common ionic liquid catalyst precursors for alkylation include imidazolium, or pyridinium-based cations coupled with the chloroaluminate anion (Al2Cl7−).
Isomerization processes utilizing ionic liquid catalysts have been developed, such as, US 2004/059173, and U.S. Pat. No. 7,053,261, for example.
Ionic liquids provide advantages over other catalysts, including being less corrosive than catalysts like HF, and being non-volatile.
However, the cost of ionic liquids has limited the widespread adoption of ionic liquids.
There is a need for lower cost ionic liquids for use in a variety of hydrocarbon conversion processes.